The OTN (Optical Transport Network) is one of the transmission technologies that support the backbone network for optical communications, and has been standardized by the ITU-T (International Telecommunication Union Telecommunication Standardization Sector).
The OTN is a technology for generating frames of a layered structure in which client signals such as SONET/SDH (Synchronous Optical Network/Synchronous Digital Hierarchy) and Ethernet™ are accommodated, and performing data transmission appropriate for WDM (Wavelength Division Multiplexing).
In recent years, there is a growing discussion on OTN extension as to how to accommodate various client signals while maintaining connectivity with the existing layered structures and how to achieve efficient data transmission.
As one example of OTN extension, a client accommodating system using LO-ODU (Lower Order Optical Channel Data Unit) and HO-ODU (Higher Order Optical Channel Data Unit) is drawing attention.
According to this system, in addition to data signals such as SONET/SDH and Ethernet, signals having a frame structure are also accommodated in a multiplexed form as client signal so as to increase the flexibility in accommodation of client signals.
The frame accommodated as a client signal is called an LO-ODU, and the frame in which the LO-ODU is stored is called an HO-ODU. The LO-ODU is mapped to a payload area of the HO-ODU so as to be transmitted. The receiving end detects frame synchronization of the LO-ODU so as to perform monitoring.
As one of related art techniques for frame synchronization, a method that performs frame synchronization for each STM-1 (Synchronous Transport Module-1) in STM-N has been disclosed (see, for example, Japanese Laid-open Patent Publication No. 08-265285). There has also been disclosed a technique that reduces the time taken to detect a fixed pattern for frame synchronization (see, for example, Japanese Laid-open Patent publication No. 2008-278137).
There are a plurality of types of LO-ODUs to be accommodated in the HO-ODU, in accordance with the transmission rate. Upon mapping the plurality of types of LO-ODUs to the HO-ODU, the LO-ODUs are discretely mapped to a payload area of the single HO-ODU. Further, upon monitoring the LO-ODUs at the receiving end, frame synchronization of the LO-ODUs is established.
For establishing frame synchronization, a selector circuit may be provided for each type of LO-ODU so as to sort LO-ODUs by type, and then synchronization detection control may be performed on the sorted LO-ODUs.
According to this circuit configuration, however, a plurality of parallel control systems for detecting frame synchronization on a per LO-ODU type basis need to be provided. Therefore, the same number of control systems as the possible maximum number of LO-ODU types are provided in advance, resulting in increased apparatus size (circuit size) and increased implementation difficulty.